The 3rd Generation Partnership Project (3GPP) is developing the architecture and protocols for the next generation (e.g., 5th Generation (5G)) wireless communication networks (e.g., new radio (NR)). An NR network strives to deliver sub-millisecond latency and at least 1 Gbps (e.g., 10 Gbps) downlink speed, and support billions of connections. In comparison, a 4th Generation (4G) wireless network, such as a legacy long-term-evolution (LTE) network, can support at most 150 Mbps downlink speed with a single carrier. Thus, an NR network may have a system capacity that is 1000 times of the capacity of the current 4G wireless network. To meet these technical requirements, the NR exploits higher frequencies of the radio spectrum in the millimeter wave range (e.g., 1 to 300 GHz) which can provide greater bandwidth.
Extensive studies have been focused on millimeter wave, directional antenna, and beamforming technologies, which are imperative to meet the anticipated 1000 times system capacity for the NR requirements. For example, millimeter wave components such as antenna array elements are found suitable for multiple spatial streams, beamforming and beam steering. However, due to high path loss of the millimeter waves, high gain directional antennas and beamforming methods need to be carefully designed to support transmission in the millimeter wave frequency range (e.g., 1 to 300 GHz). Antenna arrays having hundreds or thousands of antenna elements may be used for beamforming to reduce the high path loss of the millimeter waves. Since the number of beamforming precoding matrices is proportional to the number of antenna elements, the processing time for beam sweeping may become unbearably long. Thus, group-based beamforming precoding matrices are introduced to reduce the processing time. The beamforming precoding matrix can be separated into two categories, namely, coarse beams and refine beams. The beam-widths of the coarse beams are larger than the beam-widths of the refine beam. It is noted that the coverage area of a refine beam may be overlapped with the coverage area of a coarse beam. Each coarse beam may contain several refine beams. The refine beams may be grouped into different coarse beam groups because the refine beam direction or transmission path can be covered by the corresponding coarse beam. Coarse beam information may be visible with longer period than refine beam information. For example, the coarse beam index is a long term parameter and the refine beam index is a short term parameter.
In a 4G wireless network, such as a legacy LTE network, Downlink Control Information (DCI) is used to carry control information (e.g., such as scheduling of downlink (DL) and uplink (UL) transmission, Channel State Information (CSI) report format, and hybrid auto repeat request (HARM), and etc.) from a base station to user equipment (UE). There are several DCI configurations for carrying different information. The UE can determine the DCI configurations received from the base station based upon transmission mode (TM) and radio network temporary identifier (RNTI). That is, in the legacy LTE network, the UE would blindly decode the DCI from the base station without any knowledge of which TM and/or RNTI the DCI currently uses.
As the DCI may be composed of different numbers of control channel elements (CCEs), it may undesirably take a long time for blind decoding the DCI in the legacy LTE system. FIG. 1A illustrates a frame structure having CCEs 102 and resource elements (REs) 104 carried by a physical downlink control channel (PDCCH) 106. FIG. 1B illustrates a blind decoding process in which a UE blindly searches through different CCEs and aggregation levels (ALs) to decode the DCI. Such blind decoding process is both time consuming and power inefficient.
As the 3GPP is working on the basics of 5G NR standardization, a two-stage (or two-level) DCI format/configuration design has recently been proposed for transmitting control signals. However, the details of the two-stage DCI configuration have not yet been discussed extensively.
Thus, there is a need in the art for methods for reducing control channel overhead and transmission latency, and improve power efficiency in a wireless network using two-stage DCI formats/configurations.